1. Field of the Invention
The present invention relates to the photolithography process used in the manufacturing of semiconductor devices and the like. More particularly, the present invention relates to an exposure apparatus for exposing a layer of photoresist disposed on a substrate, and to a method of controlling the position of the substrate relative to components of the exposure apparatus during the exposure process.
2. Description of the Related Art
In general, semiconductor devices are manufactured by performing series of processes on a semiconductor substrate. These processes include a photolithography process, an ion implantation process, a deposition process, and an etching process.
Photolithography entails coating the semiconductor substrate with photoresist, exposing the photoresist to light having a predetermined wavelength and passed through a reticle, and developing the photoresist. The reticle bears a fine pattern corresponding to a pattern, e.g., a circuit pattern, to be formed on the substrate. This reticle pattern is transferred to the photoresist when the photoresist is exposed to light directed through the reticle. The developing process removes select (exposed or non-exposed) portions of the photoresist to thereby form a photoresist pattern. A fine pattern is then formed on the semiconductor substrate by etching one or more layers disposed under the photoresist pattern, i.e., by using the photoresist pattern as an etch mask. This process is repeated for several layers formed one above the other on the substrate.
The exposure apparatus for performing the exposure process includes a lens that reduces and projects an image of the pattern reticle onto the semiconductor substrate, and a device for measuring the position of the semiconductor substrate relative to the exposure apparatus so that the image of the reticle pattern can be transferred to a precise position on the layer of photoresist. The precision of the exposure process is crucial to realizing a proper alignment of the fine patterns to be formed on the layers stacked on the semiconductor substrate. Thus, the lens and the measuring device should be fixed during the exposure process while the device is measuring the relative position of the semiconductor substrate.
However, the semiconductor substrate is supported on a movable stage in the exposure apparatus, and the unit for moving the stage or external factors may induce vibrations in the lens or in the measuring device during the exposure process. If vibrations do occur, the image of the reticle pattern may not be transferred to the desired location on the semiconductor substrate. As a result, the fine patterns may not be properly aligned throughout the layers on the substrate.